1. Field of the Invention
The present invention relates to a magnetic sensor, and more particularly to a magnetic impedance sensor which is a high-sensitive magnetic sensor.
2. Description of the Related Art
As information devices and measuring and control devices are being rapidly developed in recent years, demand of magnetic sensors which are low in size and costs and high in sensitivity and response speed have increased more and more. For example, in a hard disc device of an external memory device for a computer, a high performance has been advanced such that an induction type magnetic head of the bulk type has been changed to a thin-film magnetic head or a magnetic resistance effect (MR) head. Since in a rotary encoder which is a rotary sensor for use in a motor, a magnetic ring having a high magnetic density has been demanded, there has been required a magnetic sensor which is capable of detecting a fine surface magnetic flux with a high sensitivity instead of the conventional magnetic resistance effect (MR) sensor used. Also, demand of high-sensitive sensor which can be used for a non-destructive investigation or a bill investigation has increased more and more.
As representative magnetic detecting elements which are now being used, there are an induction type reproduction magnetic head, a magnetic resistance effect (MR) element, a flax gate sensor, a hall element and so on. Also, in recent years, there have been proposed magnetic sensors high in sensitivity using the magnetic impedance effect of an amorphous wire (refer to Japanese Patent Laid-open Publication No. Hei 6-176930, Japanese Patent Laid-open Publication No. Hei 7-181239, Japanese Patent Laid-open Publication No. Hei 7-333305) or the magnetic impedance effect of a magnetic thin-film (refer to Japanese Patent Laid-open Publication No. Hei 8-75835, Japanese Applied Magnetic Institute Journal, vol. 20,553 (1996)).
The induction type reproduction magnetic head suffers from such problems that a magnetic head per se becomes large-sized because a coil winding is required, to the contrary, that the sensitivity of detection is remarkably deteriorated in case the number of turns of coil is reduced for the purpose of making the magnetic head small. On the other hand, the magnetic resistance effect (MR) element using a ferromagnetic film is being employed. The MR element is so designed as to detect not a temporal variation in magnetic flux but the magnetic flux per se, to thereby advance the miniaturizing of the magnetic head. However, even in the existing MR element, for example, the MR element using a spin valve element, the rate of change in the electric resistance is small to the degree of 6% or less at the maximum, and the external magnetic field necessary for obtaining the resistance change of several % is large to the degree of 1.6 kA/m or more. Therefore, the magnetic resistance sensitivity is low to the degree of 0.001%/(A/m) or less. Also, in recent years, there has been found a giant magnetic resistance effect (GMR) due to an artificial lattice in which the rate of change in the magnetic resistance is several tens %. However, in order to obtain the resistance change of several tens %, the external magnetic field of several tens A/m is necessary, and therefore the practical use of the magnetic resistance element as a magnetic sensor has not been realized.
The flux gate sensor which is the conventional high-sensitivity magnetic sensor is so designed as to measure the magnetism by using the phenomenon in which the symmetric B-H characteristic of a high permeability magnetic core such as a permalloy is changed according to the external magnetic field, and has the high resolution and the high directivity of 1. However, the above flux gate sensor suffers from such problems that a large-sized magnetic core is required in order to enhance the sensitivity of detection, that it is difficult to reduce the dimensions of the entire sensor and that the power consumption is large.
The magnetic sensor using a hail element is a sensor using a phenomenon in which when a magnetic field is applied perpendicularly to a surface of the sensor into which a current flows, an electric field is developed in a direction perpendicular to both of the current flowing direction and the magnetic field applying direction, to thereby induce an electromotive force in the hall element. The hall element is advantageous in the costs but has such defects that the sensitivity of the magnetic field detection is low and that the temperature characteristic of the magnetic field sensitivity is low because the mobility of electrons or positive holes is changed by diffusion of lattices within the semiconductor due to thermal vibrations to a change of temperature since the hail element is made of semiconductor such as Si or GaAs.
Japanese Patent Laid-open Publication No. Hei 6-176930, Japanese Patent Laid-open Publication No. Hei 7-181239 and Japanese Patent Laid-open Publication No. Hei 7-333305 have proposed therein magnetic impedance elements by which a great improvement in the magnetic field sensitivity has been realized. The magnetic impedance element is a magnetic impedance element that has a basic principle in which only a voltage caused when a circumferential magnetic flux changes as a time elapses, which is produced when a current which varies as a time elapses is supplied to a magnetic line is detected as a change caused by the externally applied magnetic field. FIG. 16 shows an example of the magnetic impedance element. In the magnetic impedance element 1 of FIG. 16, an amorphous wire (a wire which has been tension-annealed after having been drawn) which is made of FeCoSiB or the like and about 30 xcexcm in the diameter of exciting distortion is employed as a magnetic line 2. FIG. 17 is a graph showing the applied magnetic field dependency of the wire (for example, the magnetic line 2 in FIG. 16) with respect to the impedance change. Even in a wire having a small dimension of about 1 mm in length, when a high-frequency current of about 1 MHz is supplied to the wire, the amplitude of a voltage across the wire changes with the high sensitivity of about 0.1%/(A/m) which is 100 times or more of the MR element.
As the magnetic sensor, there has been demanded a high-sensitive magnetic sensor which is small in size, low in the costs and excellent in the linearity and the temperature characteristic of an output to the detected magnetic field. The magnetic sensor using the magnetic impedance effect of the amorphous wire exhibits the magnetic field detection characteristic of a high sensitivity. Also, Japanese Patent Laid-open Publication No. Hei 6-176930 and Japanese Patent Laid-open Publication No. Hei 6-347489 disclose that the application of a bias magnetic field allows the linearity of the dependency of the applied magnetic field on the impedance change to be improved; and that a negative feedback coil is wound on the amorphous wire, and a current proportional to a voltage between both ends of the amorphous wire is supplied to the coil to conduct negative feedback, thereby being capable of providing a sensor (high-sensitive magnetic impedance element) which is excellent in linearity and uniform in the magnetic field detection sensitivity with respect to the temperature change of the sensor section.
However, because the high-sensitive magnetic impedance element is formed of the amorphous wire the diameter of which is about 30 xcexcm, it is not proper for fine machining, thereby making it difficult to provide a super-miniaturized magnetic detecting element. Also, since both of the bias coil and the negative feedback coil must be prepared by winding a thin copper wire, there is a limit of miniaturizing the high-sensitive magnetic impedance element, and there also arises a problem from the viewpoint of productivity such that the soldering property of the electrode is low since an oxide film is formed on the surface of the wire.
In addition, if the length of the element is lengthened in order to increase the impedance of the element for the purpose of obtaining a large sensor output, it is not proper for the miniaturization of the magnetic sensor. On the other hand, there is proposed that the wire is bent in a zigzag manner for use. However, in this case, since the wire made of a magnetic material is bent, the magnetic characteristic is deteriorated by a strain stress with the result that a sensor output is remarkably degraded. Also, there is proposed that a wire is divided into a plurality of pieces, the divided wires are disposed in parallel and electrically connected in series. However, in this case, there arises a problem of productivity such as a problem of electrode soldering.
On the other hand, as an attempt to miniaturize the magnetic impedance element, there has been proposed a magnetic impedance element using a magnetic thin-film in Japanese Patent Laid-open Publication No. Hei 8-75835, by which the element is going to be miniaturized. Also, the present inventors have proposed a miniaturized magnetic impedance element in which a thin-film coil is wound around a thin-film magnetic core three-dimensionally to provide a bias coil and a negative feedback coil in Japanese Patent Application No. Hei 9-269084. However, the magnetic film of those proposed elements is of a single-layer structure.
In this case, if the variation amount xcex94 Z/Z of the impedance and the width and the thickness of the element are kept constant in order to take a large sensor output, that is, in order to take a large variation amount xcex94 Z of the impedance, the length of the element must be lengthened. For that reason, there arises such a problem that the entire chip size becomes large.
Although the details will be described with reference to embodiments of the present invention, a magnetic domain structure shown in FIG. 3A is ideal, and in fact, when a uniaxial anisotropy is given in the widthwise direction of a single-layer thin-film pattern, a diamagnetic field is developed in the widthwise direction, and in order to minimize the diamagnetic energy, the magnetic domain structure becomes a state where the magnetic vector is closed as shown in FIG. 5. However, when the magnetization vector is directed to the longitudinal direction of the thin-film pattern, since a magnetic permeability xcexcxcex8 in the widthwise direction due to the external magnetic field Hex is hardly changed, the MI effect becomes very small. In other words, the MI effect of the 90xc2x0 magnetic domain portion shown in FIG. 5 is very small so that the MI effect of the entire thin-film becomes small.
Also, as shown in FIG. 3 on pages 66 to 69 of xe2x80x9cElectronic Technologyxe2x80x9d (Nikkan Kogyo Shinbunsha) 1992-December, there has been proposed a magnetic impedance (MI) element in which the length of a magnetic core is lengthened by bending a magnetic thin-film in a zigzag manner. However, in this structure, a magnetic domain structure at curved portions is complicated, and when a magnetic field is applied to the magnetic impedance element from the external, the magnetic walls of the curved portions cause noises due to a rapid change of the output voltage from the element which is caused by Barkhausen jump which ununiformly moves.
Further, there has been proposed a magnetic sensor which is structured such that a pair of magnetic detecting sections each of which is made up of an amorphous wire and a coil for applying a bias magnetic field to the wire are disposed in parallel to conduct differential drive, thereby improving the sensitivity, in Japanese Patent Laid-open Publication No. Hei 7-248365.
However, because the high-sensitive magnetic impedance element is formed of the amorphous wire which is about 30 xcexcm in diameter, it is not proper for fine machining, as a result of which it is difficult to provide a super-miniaturized magnetic detecting element. Also, since both of a bias coil and a negative feedback coil must be prepared by winding a thin copper wire, there is a limit of miniaturizing the high-sensitive magnetic impedance element and there also arises a problem from the viewpoint of productivity such that the soldering property of the electrode is low since an oxide film is formed on the surface of the wire. In particular, as disclosed in Japanese Patent Laid-open Publication No. Hei 7-248365, in case of the differential drive, because two magnetic detecting elements are employed, the miniaturizing of the magnetic impedance element becomes increasingly difficult, and the productivity is also deteriorated. In addition, because the bias coil and the negative feedback coil must be wound around the respective amorphous wires, an interval between two wires requires a space for winding the coil, and the distance between those wires becomes long as much, thereby making it difficult to accurately detect a small local magnetic field.
On the other hand, as an attempt to miniaturize the magnetic impedance element, there has been proposed a magnetic impedance element using a magnetic thin-film in Japanese Patent Laid-open Publication No. Hei 8-75835, by which the element is going to be miniaturized. Also, the present inventors have proposed a miniaturized magnetic impedance element in which a thin-film coil is wound around a thin-film magnetic core three-dimensionally to provide a bias coil and a negative feedback coil in Japanese Patent Application No. Hei 9-269084. However, even in those inventions, two chips must be used in order to employ those inventions in a differential drive circuit. For that reason, because an interval between two thin-film magnetic cores becomes long, it is difficult to accurately detect a small local magnetic field similarly as in the amorphous wire.
The present invention has been made in view of the above circumstances, and therefore an object of the present invention is to provide a high-sensitive magnetic sensor element which is small in size, low in the costs, high in output and excellent in the linearity and the temperature characteristic of an output detecting magnetic field with the above magnetic sensor.
In order to achieve the above object of the present invention, according to a first aspect of the present invention, there is provided a magnetic impedance element including a substrate made of a non-magnetic material, a thin-film magnetic core formed on said substrate, and first and second electrodes disposed on both ends of said thin-film magnetic core in a longitudinal direction thereof, characterized in that said thin-film magnetic core is formed by laminating a plurality of magnetic films through non-magnetic thin-films.
According to a second aspect of the present invention, there is provided a magnetic impedance element as defined in the first aspect of the present invention, characterized in that the thin-film magnetic core is formed by laminating the plurality of magnetic films, the thickness of which is equal to each other.
According to a third aspect of the present invention, there is provided a magnetic impedance element as defined in the first aspect of the present invention, characterized in that the thickness of the laminated magnetic films is ununiform.
According to a fourth aspect of the present invention, there is provided a magnetic impedance element as defined in the first aspect of the present invention, characterized in that the plurality of magnetic films are laminated through non-magnetic thin-films, and the total amount of products of the thickness and the magnetization amplitudes of the respective odd magnetic films is nearly equal to the total amount of products of the thickness and the magnetization amplitudes of the respective even magnetic films.
According to a fifth aspect of the present invention, there is provided a magnetic impedance element as defined in the first, second, third or fourth aspect of the present invention, characterized in that the non-magnetic films interposed between the respective magnetic films are made of an electrically conductive material.
According to a sixth aspect of the present invention, there is provided a magnetic impedance element as defined in the first, second, third or fourth aspect of the present invention, characterized in that the non-magnetic films interposed between the respective magnetic films are made of an insulator, and both end portions of the laminated magnetic films are electrically connected to each other at both end sides thereof.
According to a seventh aspect of the present invention, there is provided a magnetic impedance element as defined in the first aspect of the present invention, characterized in that said magnetic films that constitute the thin-film magnetic core are formed of a plating film made of at least one selected from a group consisting of NiFe, CoFe, NiFeP, FeNiP, FeCoP, FeNiCoP, CoB. NiCoB, FeNiCoB, FeCoB and CoFeNi.
According to an eighth aspect of the present invention, there is provided a magnetic impedance element as defined in the first aspect of the present invention, characterized in that said magnetic films that constitute the thin-film magnetic core are formed of an amorphous sputter film which is made of CoZrNb, FeSiB or CoSiB.
According to a ninth aspect of the present invention, there is provided a magnetic impedance element as defined in the first aspect of the present invention, characterized in that said magnetic films that constitute the thin-film magnetic core are formed of an NiFe sputter film.
In the invention thus structured, there can be provided the thin-film magnetic impedance element having a uniaxial anisotropy in the widthwise direction, in which the non-magnetic films are interposed in the magnetic thin-film to provide at least two layers of the magnetic thin-films, with the result that the magnetrostatic coupling allows the magnetization vector of the upper and lower magnetic films to be coupled to each other, thereby coming to a magnetic close state. With this state, the inner magnetic energy of the thin-film becomes minimized, and the thin-film having a two-layer structure is made up of only 180xc2x0 magnetic domain, as a result of which the MI effect is larger than that of the single-layer film. From the above viewpoints, the high-sensitive magnetic impedance element can be provided.
According to a tenth aspect of the present invention, there is provided a magnetic impedance element including a substrate made of a non-magnetic material and a thin-film magnetic core formed on said substrate and having electrodes on both ends of said thin-film magnetic core in a longitudinal direction thereof, characterized in that at least two of said thin-film magnetic cores are disposed in parallel, and said respective thin-film magnetic cores are electrically connected in series to each other.
With the above structure in which at least two of said thin-film magnetic cores are disposed in parallel, and in case said respective thin-film magnetic cores are electrically connected in series to each other, the impedance of the magnetic impedance element can be increased without increasing the entire chip size, thereby being capable of increasing a sensor output.
According to an eleventh aspect of the present invention, there is provided a magnetic impedance element as defined in the tenth aspect of the present invention, characterized in that said thin-film magnetic core has a thin-film bias coil and a thin-film negative feedback coil formed through an insulator, said thin-film bias coil and said thin-film negative feedback coil are alternately wound on the same plane at a given interval in the same direction and also they are wound by the same number of turns.
The above magnetic impedance element is structured in such a manner that the thin-film coil for bias and the thin-film coil for negative feedback are wound around the thin-film magnetic cores which are disposed in parallel through the insulator. The structure makes it possible to miniaturize the magnetic sensor and to make mass production. Also, because the thin-film coil produced with the above structure is excellent in coil efficiency, a required bias magnetic field is obtained with a small amount of current, and the linearity of an output to the magnetic field can be improved with a small amount of negative feedback. Also, since the thin-film coil for bias and the thin-film coil for negative feedback are alternately wound on the same plane, the bias magnetic field and the negative feedback magnetic field can be uniformly applied to the respective portions of the thin-film magnetic cores, to thereby stabilize the characteristics of the magnetic sensor.
According to a twelfth aspect of the present invention, there are provided two magnetic impedance elements from which a differential output is extracted in such a manner that two longitudinal thin-film magnetic cores formed on a substrate made of a non-magnetic material are disposed in parallel, first and second electrodes are disposed on both ends of the respective thin-film magnetic cores, and a thin-film bias coil and a thin-film negative feedback coil which are alternately wound on the same plane by the same number of turns in the same direction are disposed on said thin-film magnetic cores at a given interval through an insulator.
According to a thirteenth aspect of the present invention, there are provided two magnetic impedance elements as defined in the twelfth aspect of the present invention, characterized in that the respective thin-film magnetic cores of the two magnetic impedance elements formed on said non-magnetic substrate are formed of at least two thin-film magnetic cores which are disposed in parallel and electrically connected in series with each other.
According to a fourteenth aspect of the present invention, there are provided two magnetic impedance elements as defined in the twelfth aspect of the present invention, characterized in that in said two magnetic impedance elements, the respective one electrodes of the first and second electrodes of the thin-film magnetic cores, the thin-film bias coil electrode and the thin-film negative feedback coil electrode are commonly connected to each other.
According to a fifteenth aspect of the present invention, there are provided a magnetic impedance element in which a longitudinal thin-film magnetic core is formed on a substrate made of a non-magnetic material, first and second electrodes are disposed on both ends of said thin-film magnetic core in a longitudinal direction thereof, a third electrode is disposed at a middle point of said thin-film magnetic core and a thin-film bias coil and a thin-film negative feedback coil which are alternately wound on the same plane at the same number of turns in the same direction are disposed on said thin-film magnetic core at a given interval through an insulator, and a differential output is extracted from said first and second electrodes.
Because the above structure makes it possible to produce the magnetic sensor element for differential driving, a local magnetic field can be accurately detected, and also the magnetic sensor element for differential driving can be produced without increasing the entire chip size, thereby being capable of miniaturizing the magnetic sensor and making mass production.
According to a sixteenth aspect of the present invention, there are provided a magnetic impedance element as defined in the fifteenth aspect of the present invention, characterized in that the respective one electrodes of the third electrode of said thin-film magnetic core and the electrodes of the thin-film bias coil and the thin-film negative feedback coil are commonly connected to each other.
The above structure can make an interval between the two thin-film magnetic cores that form a sensor head constant and narrow and can manufacture the magnetic sensor element for differential driving without increasing the entire chip size, thereby being capable of miniaturizing the magnetic sensor and making mass production.
According to a seventeenth aspect of the present invention, there are provided a magnetic impedance element as defined in any one of the first, second and twelfth to sixteenth aspects of the present invention, characterized in that said thin-film magnetic core is formed of a plating film made of at least one selected from a group consisting of NiFe, CoFe, NiFeP, FeCoP, CoB, NiCoB, FeNiCoB, FeCoB and CoFe.
According to an eighteenth aspect of the present invention, there are provided a magnetic impedance element as defined in any one of the first, second and twelfth to sixteenth aspects of the present invention, characterized in that said thin-film magnetic core is formed of an amorphous sputter film made of any one selected from CoZrNb, FeSiB and CoSiB or an NiFe sputter film.
Further, in the above magnetic impedance element, with the structure in which a portion that forms an earth electrode out of the electrode of the thin-film magnetic core, the electrode of the thin-film bias coil and the electrode of the thin-film negative feedback coil is made common, the number of process for connecting the magnetic impedance element to a sensor drive circuit due to wire bonding or the like in a sensor module manufacturing process can be reduced.
Also, because the thin-film coil manufactured with the above structure is excellent in coil efficiency, a required bias magnetic field is obtained with a small amount of current, and the linearity of an output to the magnetic field can be improved with a small amount of negative feedback. Also, since the thin-film coil for bias and the thin-film coil for negative feedback are alternately wound, the bias magnetic field and the negative feedback magnetic field can be uniformly applied to the respective portions of the thin-film magnetic cores, to thereby stabilize the characteristics of the magnetic sensor.
The magnetic impedance element according to the present invention is structured in such a manner that the thin-film magnetic core is formed on the non-magnetic substrate, and the electrodes are disposed on both ends of the thin-film magnetic core in a longitudinal direction thereof. The magnetic impedance element according to the present invention is structured by laminating a plurality of magnetic films made of at least one of a group consisting of NiFe, CoFe, NiFeP, FeNiP, FeCoP, FeNiCoP, CoB, NiCoB, FeNiCoB, FeCoB and CoFeNi. Also, in the case where an amorphous material is selected as the magnetic film, any one of CoZrNb, FeSiB and CoSiB is selected.
The non-magnetic film is disposed between the magnetic films of the magnetic impedance element of the present invention, and the non-magnetic film is made of an electric conductive material or an insulator.
At least two thin-film magnetic cores are disposed on the non-magnetic substrate in parallel, the thin-film bias coil and the negative feedback coil are formed on the above thin-film core through the insulator, and those coils are alternately wound on the same plane in the same direction. The respective one electrodes of the electrodes provided on the above thin-film bias coil and the negative feedback coil are connected to each other. The present invention is structured such that two magnetic impedance elements are disposed to extract a differential output.
At least two thin-film magnetic cores which are disposed in parallel on the above non-magnetic substrate are electrically connected in series with each other.